In the description of the background of the present disclosure that follows, reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
In drilling, for instance, the tool is given a rectilinear axial feeding motion. The proper tool body may, for instance, consist of a shaft-type cutter, an end mill or a drilling tool. Common for these is that they usually carry a plurality of cutting plates of a hard material, such as cemented carbide. Said cutting plates are usually of an indexable insert type, i.e., they may be loosened and turned or “be re-indexed” when a cutting edge has been worn out and the operator desires to advance a new cutting edge in the operative position by turning. In order to achieve a fine and smooth surface in the workpiece, it is necessary that the operative cutting edges of the cutting inserts describe substantially identical rotation paths, i.e., in, for instance, a shaft-type cutter or an end mill, they should have substantially the same axial and radial position in the milling body. This makes, among other things, exceptionally heavy demands on precision of the production of the cutting seats in the milling body. If, for instance, the axial positioning is unsatisfactory, so-called axial runout arise, which lead to worsen consequences.
Furthermore, today's modern tools are exposed to very strong chip wear, which imposes greater requirements on the hardness of the surface of the holder body, especially at the material portions thereof that are located next to the cutting seats and that are exposed to direct chip contact in the machining. It is, above all, the surface of the holder body being closest to the cutting seat straight opposite in the direction of circumference that will be strongly exposed to this wear.
Furthermore, now greater requirements are imposed on fatigue strength of the material in the tool body, since they become more and more optimized in the design thereof.
A known way to increase the fatigue strength of the material is to provide compressive stresses in the surface by surface hardening the material, e.g., by nitriding, nitrogen alone being transferred to the surface of the holder body, usually steel, in a gas atmosphere, essentially at a temperature of 510–550° C. Another way is to subject the material to nitrocarburizing, carbon and nitrogen being transferred to the surface in a gas atmosphere, normally at a temperature of approximately 570° C. An additional known way is to submit the material to so-called ion nitriding, when nitrogen alone is transferred to the surface in an ionized gas, under almost vacuum, at a temperature of approximately 450 to 650 C.
An additional known way to increase the fatigue strength of the material is to provide compressive stresses and improve the surface quality of the material by so-called micro blasting, which means that the surface of the material is bombarded with small particles in such a way that a part of the material is removed at the same time as compressive stresses are built up in the material. Another known way to increase the fatigue strength of the material by providing compressive stresses and improve the surface quality of the material is so-called shot peening, which is an established method used in order to increase the service life of metal components exposed to dynamic loads. Shot peening also prevents crack formation caused by stress corrosion. The idea of the method is to bombard, under accurately controlled forms, the surface with spherical particles of, for instance, steel, glass or ceramics.